This invention relates to three phase windings for high voltage machines with Y-connected phases generally, and more particularly to an improved winding arrangement for a machine of this nature which has coil groups disposed along the circumference cyclically distributed, each consisting of several series connected coils, the magnetic flux of which points alternatingly in opposite directions.
In the conventional three phase, high voltage windings with coil groups connected in series and/or in parallel within each phase the individual coil groups are always series connected in the same manner so that the direction of the magnetic flux through all coil groups is either the same as the direction of increase in potential or opposite to it. The number of coils in a coil group is ##EQU1## N being the number of slots, m the number of phases and 2p the number of poles.
In such windings, when the coil groups are series connected, the maximum voltage at the phase alternation has the lowest value of 0.76.times.U.sub.N (U.sub.N =supply voltage) at 2p=2, which increases with an increasing number of poles to 0.88 U.sub.N at 2p=4; 0.92 U.sub.N at 2p=6; 0.94 U.sub.N at 2p=8 to almost U.sub.N for high numbers of poles. Such high voltages always occur in parallel connected coil groups. To manage this voltage stress occurring in the coil head between adjacent coil legs at the phase transition, considerably greater minimum leg spacings are required in view of the corona set-in voltage than would be necessary for production of ventilation reasons. This increases the coil length, the copper weight and the space requirement of the windings.